Are you judging your dps on your overall dps for the instance? If you are, it might simply be that other classes are AoEing more than you. What's really important is your dps on boss fights, so judge by that.
If you DO want high overall dps, make sure you're using seal of command. As soon as tank has aggro, get divine storm on CD, consecration, and then judge for mana, then prioritize judgment when it's up, then divine storm, then consecration. Most packs won't live through a rotation or two, but everyone AoEs down all instances now because of how classes work in WotLK. If you're not hitting a few mobs at once, it literally halfs or worse your dps output.
I've been doing a death knight in the 60's and I'm nearly always top dps even though my gear is **** (on a new server, no heairloom gear nor money to twink), because I prioritize the AoE abilities like no other. :P Except on bosses of course. But if you were to just measure on bosses, I'd probably rarely be first. killing machine proc+howling blast = kaboom.
Like I said though, all that really is moot if you can't put out decent dps on bosses.
EDIT: on yeah, also if you do buy some gear, plate with strength on it is very expensive. Chain with strength on it is very cheap. Leather with strength even cheaper, and in BC levels, there's plenty of it. You're a dps, not a tank, don't be afraid to wear lower armor value gear. Lastly, gem slots trump all else because BC gear wasn't made with WotLK gems in mind. Even blue gems in a gem slot are way overpowered. To this day, I don't understand why they didn't put level limits on gems, but they didn't, so exploit it.
EDIT TO MY EDIT: By blue gems, I mean rare gems instead of epic gems. I don't mean +Stamina gems.
Edited, Jun 6th 2010 2:42pm by digitalcraft